This invention relates generally to a multilayer film, a meat product package comprising an enclosing multilayer film and an insitu aqueous medium--cooked meat product, i.e., the cook-in type, and a method for preparing a cooked meat product. In the method of the invention the meat is placed in a flexible tube formed of this film, hermetically sealed and insitu cooked by an aqueous medium. During the insitu cooking, the film is against the meat outer surface in contiguous adhering relation therewith.
There are numerous requirements for a multilayer cook-in shrink film including: delamination resistance, low oxygen permeability, and high temperature strength. For certain end uses as for example packaging of chunked and formed meat products for cook-in, the film should provide heat shrinkability representing about 30-50% shrinkability at about 90.degree. C. Another very desirable characteristic for meat cook-in shrink films is adherence to the meat outer surface thereby preventing "cook-out", which is the collection of juices between the meat outer surface and film inner surface.
Probably the most commonly used inner layer in multilayer barrier-type shrink films is ethylene vinyl acetate. However, the prior art has recognized that ethylene vinyl acetate does not provide good meat adhesion. For example, Judd et al U.S. Pat. No. 4,463,778 teaches that regenerated cellulose casings may be internally treated with vinyl acetate polymer to produce a coating which causes the casing to adhere to dry sausage emulsion and follow the sausage shrinkage during curing, but provide a low level of meat adhesion. In this manner the coating readily releases from the dried sausage emulsion when the casing is separated therefrom.
Because of the notoriously poor adhesion of ethylene vinyl acetate to meat, the prior art has employed various coatings or layers between an EVA substrate and the meat to provide good adhesion. Also, the prior art has developed a number of multilayer plastic cook-in films and certain of these are in commercial use. For example Bieler et al U.S. Pat. No. 4,104,404 describes a ten layer film comprising four central nylon layers, an ionomer layer on each outer side of the central layers, and two outer polyethylene layers on each outer side of the ionomer layers. The patentee demonstrates that delamination of the outer polyethylene layer under cook-in conditions was only avoided by irradiation dosage of the entire multilayer film at a level of at least 6 MR. This film does not appear to provide high meat adhesion.
Another commercially employed cook-in film is the type described in Oberle et al U.S. Pat. No. 4,469,742, also comprising six layers irradiated to dosage of at least 6 MR. The central barrier layer is hydrolyzed ethylene-vinyl acetate copolymer (EVOH), chosen because of its higher softening point and superior oxygen barrier properties as compared to the saran-type barrier layer commonly used in multilayer films for ambient temperature applications. On each side of the barrier layer is an adhesive layer such as chemically modified polyethylene, eg. Plexar. On the outer side of each adhesive layer is a shrink layer such as ethylene-vinyl acetate copolymer (EVA), and the outside (abuse) layer is also the EVA type having a vinyl acetate content of about 5-12 wt.%. The innermost (heat sealing) layer may for example be a propylene-ethylene random copolymer (PER). If meat adhesion is required, an additional ionomer layer is used as the innermost layer.
One general concern in the extrusion manufacture of multilayer films containing EVOH is that the process conditions be such that gel formation is avoided. This may occur if resins are retained in the extruder passages and exposed to heat for prolonged periods so as to form oxidized particles which ultimately cause bubble breakage or appear in the finished film.
It will be apparent from the foregoing that these prior art cook-in films are complex both in terms of multiple materials and sophisticated manufacturing techniques ie. six layers and relatively high irradiation dosage level to avoid delamination. Further, some of these films do not provide meat adhesion and an additional layer is needed for this specific purpose.
Lustig et al U.S. Pat. No. 4,784,863 describes a multilayer film requiring only three layers but which overcomes many of the limitations of these earlier films requiring at least six layers. This film comprises an outer layer, a core-barrier layer and an inner EVA layer having on its inner surface at least about 4 grams/1000 ft..sup.2 of starch particles with major dimensions less than about 100 microns and being substantially uniformly dispersed across this inner surface and integral therewith. At least the dispersed starch particle-containing EVA inner surface is irradiated at dosage of at least 2 MR, preferably less than 5 MR. When used in a meat product package this film inner surface has good meat adhesion and little fat-out for most meats including premium grade boiled ham having less than about 10% fat and usually less than about 5% high collagen meat protein of the total available meat protein. Unfortunately when the meat to be cooked insitu is a commodity style boiled ham having a product composition of more than about 10% fat and usually more than about 5% high collagen meat portion of the total available meat portion, the irradiated dispersed starch particle-containing EVA inner layer-to-meat adhesion is only marginally satisfactory.
An object of this invention is to provide a flexible tube formed of multilayer film having less than six layers and with an inner layer providing improved adhering relation to high fat and/or high collagen type meat product during insitu cooking in an aqueous medium.
Another object is to provide a meat product package including an insitu aqueous medium-cooked meat product with its outer surface in improved adhering relation to the inner layer of a multilayer film having less than six layers and which satisfies the other requirements of a cook-in film.
Another object is to provide a method for preparing an insitu cooked high fat and/or high collagen meat product in a flexible tube having less than six layers, with improved adhering relation between the meat outer layer and film inner layer.
Other objects and advantages will be apparent from the ensuing disclosure and appended claims.